CN110224963B - Method and device for determining symbol timing synchronization position and storage medium - Google Patents

Method and device for determining symbol timing synchronization position and storage medium Download PDF

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CN110224963B
CN110224963B CN201910363862.3A CN201910363862A CN110224963B CN 110224963 B CN110224963 B CN 110224963B CN 201910363862 A CN201910363862 A CN 201910363862A CN 110224963 B CN110224963 B CN 110224963B
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ltf
timing synchronization
symbol timing
synchronization position
noise
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CN110224963A (en
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王军伟
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Gaotuoxunda Beijing Microelectronics Co ltd
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Alto Beam (china) Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2662—Symbol synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2662—Symbol synchronisation
    • H04L27/2663—Coarse synchronisation, e.g. by correlation

Abstract

The invention provides a method and a device for determining a symbol timing synchronization position and a storage medium, wherein the method comprises the following steps: acquiring the length of a field of a first long code part LTF in a digital signal in an Orthogonal Frequency Division Multiplexing (OFDM) digital information system; wherein the first LTF comprises a second LTF and a third LTF; respectively acquiring a first noise component of the second LTF field and a second noise component of the third LTF field; and determining a symbol timing synchronization position according to the field length, the first noise component and the second noise component. The invention solves the problem that the symbol timing synchronization is very difficult due to the pseudo multipath phenomenon existing in the receiver during the symbol timing synchronization in the related technology, and achieves the effect of accurately determining the symbol timing synchronization position.

Description

Method and device for determining symbol timing synchronization position and storage medium
Technical Field
The present invention relates to the field of communications, and in particular, to a method and an apparatus for determining a symbol timing synchronization position, and a storage medium.
Background
In a digital information broadcasting system or an interactive digital information transmission system, a signal frame transmitted by a transmitter usually includes a frame header part for frame detection, frame synchronization, carrier synchronization or symbol synchronization of a receiver. In 802.11n signaling frames, there are three frame formats, each having two parts for the header, namely an 8us STF (Short tracking Field) Field and an 8us LTF (Long tracking Field) Field. The STF field of 8us is used to implement functions such as signal detection, dc offset detection, carrier Frequency offset coarse estimation, signal power adjustment, and coarse synchronization of OFDM (Orthogonal Frequency Division Multiplexing) symbols. And the LTF field of 8us is used to implement functions such as fine estimation of carrier frequency offset, fine synchronization of OFDM symbols, and channel estimation.
In order to avoid potential Beam forming (Beam forming) in the 802.11n system, if there are multiple transmit antennas, the standard specifies that cyclic shifts in the time domain should be performed between the signals transmitted by the respective transmit antennas, which results in "pseudo multipath" phenomena at the receiver when performing symbol timing synchronization. The presence of these pseudo-multipaths makes symbol timing synchronization very difficult, especially in complex channel environments and in low signal-to-noise ratio environments. Inaccuracies in Symbol timing introduce Inter Symbol Interference (ISI) into the OFDM symbols, which has a large impact on receiver performance.
In view of the above problems in the related art, no effective solution exists at present.
Disclosure of Invention
The embodiment of the invention provides a method and a device for determining a symbol timing synchronization position and a storage medium, which are used for at least solving the problem that symbol timing synchronization is very difficult due to a pseudo multipath phenomenon existing in a receiver during symbol timing synchronization in the related technology.
According to an embodiment of the present invention, there is provided a method for determining a symbol timing synchronization position, including: acquiring the length of a field of a first long code part LTF in a digital signal in an Orthogonal Frequency Division Multiplexing (OFDM) digital information system; wherein the first LTF comprises a second LTF and a third LTF; respectively acquiring a first noise component of the second LTF field and a second noise component of the third LTF field; and determining a symbol timing synchronization position according to the field length, the first noise component and the second noise component.
According to another embodiment of the present invention, there is provided an apparatus for determining a symbol timing synchronization position, including: the first acquisition module is used for acquiring the field length of a first long code part LTF in a digital signal in an Orthogonal Frequency Division Multiplexing (OFDM) digital information system; wherein the first LTF comprises a second LTF and a third LTF; a second obtaining module, configured to obtain a first noise component of the second LTF field and a second noise component of the third LTF field respectively; and the determining module is used for determining the symbol timing synchronization position according to the field length, the first noise component and the second noise component.
According to a further embodiment of the present invention, there is also provided a storage medium having a computer program stored therein, wherein the computer program is arranged to perform the steps of any of the above method embodiments when executed.
According to the invention, the symbol timing synchronization position is determined by acquiring the first noise component of the second LTF field and the second noise component of the third LTF field in the digital signal and the field length of the first LTF, so that the problem that the symbol timing synchronization is very difficult due to the pseudo multipath phenomenon existing in the receiver during the symbol timing synchronization in the related technology is solved, and the effect of accurately determining the symbol timing synchronization position is achieved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
FIG. 1 is a flow chart of a method of determining a symbol timing synchronization position according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a frame structure of a digital signal in an OFDM digital information system according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an 802.11n frame format according to an embodiment of the invention;
fig. 4 is a schematic diagram of LTFs for a frame header portion of a Greenfield format frame transmitted by 4 transmit antennas in accordance with an embodiment of the present invention;
FIG. 5 is a graph illustrating a noise power curve within a symbol timing synchronization range according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a partial frame header structure in a Greenfield frame format according to an embodiment of the present invention;
FIG. 7 is a diagram illustrating the LTF cross-correlation results obtained for Non-HT mode, in accordance with an embodiment of the present invention;
FIG. 8 is a diagram illustrating the LTF cross-correlation results obtained for HT mode according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of finding a synchronized position reference using a sliding window, in accordance with an embodiment of the present invention;
fig. 10 is a schematic structural diagram of an apparatus for determining a symbol timing synchronization position according to an embodiment of the present invention.
Detailed Description
The invention will be described in detail hereinafter with reference to the accompanying drawings in conjunction with embodiments. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.
Example 1
In this embodiment, a method for determining a symbol timing synchronization position is provided, and fig. 1 is a flowchart of a method for determining a symbol timing synchronization position according to an embodiment of the present invention, as shown in fig. 1, the flowchart includes the following steps:
step S102, acquiring the length of a field of a first long code part LTF in a digital signal in an Orthogonal Frequency Division Multiplexing (OFDM) digital information system; wherein the first LTF comprises a second LTF and a third LTF;
step S104, respectively acquiring a first noise component of a second LTF field and a second noise component of a third LTF field;
and step S106, determining the symbol timing synchronization position according to the field length, the first noise component and the second noise component.
Through the above steps S102 to S104 of this embodiment, the symbol timing synchronization position is determined by obtaining the first noise component of the second LTF field and the second noise component of the third LTF field in the digital signal, and the field length of the first LTF, so that the problem that the symbol timing synchronization is very difficult due to the pseudo multipath phenomenon existing in the receiver during the symbol timing synchronization in the related art is solved, and the effect of accurately determining the symbol timing synchronization position is achieved.
In an alternative implementation manner of this embodiment, for step S106 in this embodiment, the symbol timing synchronization position may be determined by:
Figure BDA0002047619230000041
wherein the content of the first and second substances,
Figure BDA0002047619230000042
is the noise power at symbol timing synchronization position N, N is the field length of the first LTF,
Figure BDA0002047619230000043
and
Figure BDA0002047619230000044
to connect toReceived field data, ω, for the second LTF and the third LTF1And ω2A first noise component and a second noise component; n and N are positive integers;
then, a plurality of first noise components and second noise components are obtained based on different values of n, and then a plurality of noise powers are obtained
Figure BDA0002047619230000045
The value of (1) is obtained; from multiple noise powers
Figure BDA0002047619230000046
Is determined from the value-taking result
Figure BDA0002047619230000047
The value of n at the minimum is the symbol timing synchronization position.
That is, the noise power can be determined by the above equation 1, and when the noise power is selected as the minimum value, the value of n is taken as the symbol timing synchronization position.
Based on the above formula (1), the alternative implementation manner of this embodiment may further include the following three manners for determining the symbol timing synchronization position:
mode 1:
in the case where the multipath delay spread of the channel does not exceed the length of the signal cycle SIG CP in the digital signal, the symbol timing synchronization position can be determined in the following manner based on the manner in step S106 and equation 1:
first, use N/4 data points before the synchronization position N
Figure BDA0002047619230000051
Figure BDA0002047619230000052
Replacing received data points rn + N-1, rn + N-2, …, rn + 3. N/4 in the digital signal; based on the above substitution of data points, equation 1 transforms to equation 2 as follows:
Figure BDA0002047619230000053
wherein M is more than or equal to 0 and less than or equal to N-G, and G is the length of SIG CP;
then, a plurality of first noise components and second noise components are obtained based on different values of n, and then a plurality of noise powers are obtained
Figure BDA0002047619230000054
The value of (1) is obtained; from multiple noise powers
Figure BDA0002047619230000055
Is determined from the value-taking result
Figure BDA0002047619230000056
The value of n at the minimum is the symbol timing synchronization position.
Mode 2:
based on the manner in step S106 and equation 1, the symbol timing synchronization position can be determined in the following manner:
first, in the received data
Figure BDA0002047619230000057
Instead of in equation (1)
Figure BDA0002047619230000058
By using
Figure BDA0002047619230000059
Figure BDA00020476192300000510
Instead of rLTF2k in equation (1), equation 3 is obtained:
Figure BDA00020476192300000511
g is the length of other CPs except the frame header LTF CP in the digital signal;
further, use
Figure BDA00020476192300000512
Instead of in equation (1)
Figure BDA00020476192300000513
Use of
Figure BDA00020476192300000514
As in formula (1)
Figure BDA00020476192300000515
Equation 4 is obtained:
Figure BDA00020476192300000516
equation 5 is derived from equation 3 and equation 4:
Figure BDA0002047619230000061
wherein α is 1;
finally, a plurality of first noise components and second noise components are obtained based on different values of n, and then a plurality of noise powers are obtained
Figure BDA0002047619230000062
The value of (1) is obtained; from multiple noise powers
Figure BDA0002047619230000063
Is determined from the value-taking result
Figure BDA0002047619230000064
The value of n at the minimum is the symbol timing synchronization position.
Mode 3:
in the case of multiple transmit antennas, the symbol timing synchronization position is determined based on the above by:
first, local LTF symbols are combined
Figure BDA0002047619230000065
And receiving the signal
Figure BDA0002047619230000066
Sliding cross-correlation is performed within a certain range to obtain formula 6:
Figure BDA0002047619230000067
wherein represents conjugation;
the energy in the current window Ω (n) is calculated by equation 7:
Figure BDA0002047619230000068
further, obtaining a plurality of first noise components and second noise components based on different values of n, and further obtaining value results of energy omega (n) in a plurality of current windows; and determining the value of n as the symbol timing synchronization position when the energy omega (n) is maximum from the value taking results of the energy omega (n) in the current windows.
The present application will be described in detail with reference to specific embodiments of the present example;
in this embodiment, a method for finding a position with minimum noise power or a position with maximum signal-to-noise ratio to determine an optimal fine symbol synchronization position is provided. The method can be divided into three modes, wherein the first mode is to use an LTF field to find a symbol fine synchronization position; the second method is to use the data of the back part of the STF and the data of the LTF to find the fine synchronization position of the symbol; and the third method is that the cross-correlation result of the LTF field of the received signal and the locally generated LTF symbol is utilized to find several possible fine synchronization positions of the symbol, the noise power at the several possible fine synchronization positions of the symbol is obtained by utilizing the first or the second method, and the position with the minimum corresponding noise power is selected as the fine synchronization position of the symbol.
By the specific implementation mode, the method can not be influenced by the pseudo multipath phenomenon, and for an 802.11n system, the method is not influenced by the number of transmitting antennas of a transmitter, and can also be used in other systems without the pseudo multipath phenomenon; the method has good performance in a complex channel environment and a low signal-to-noise ratio environment.
Fig. 2 is a diagram illustrating a frame structure of a digital signal in an OFDM digital information system according to an embodiment of the present invention, where as shown in fig. 2, a frame header includes two parts, an STF and an LTF, and an LTF field includes two identical OFDM symbols, i.e., LTF1 and LTF2, and the LTF field includes a cyclic prefix LTF CP.
In a multipath channel environment, if the delay spread of the STF field is located in the shaded area in fig. 2, the optimal symbol timing synchronization position for the LTF1 symbol is located in the area of length L. If the synchronization position of LTF1 is shifted to the left, multipath spreading of the STF field may be introduced, resulting in inter-symbol interference (ISI). Similarly, if the synchronization position of LTF1 is shifted to the right, then some data points in SIGCP are used as LTF2 data, which also causes ISI.
Assuming no carrier frequency offset exists, the power of a noise can be obtained at the symbol timing synchronization position n by the formula (8)
Figure BDA0002047619230000071
Where N is the length of the LTF field,
Figure BDA0002047619230000072
and
Figure BDA0002047619230000073
for the received LTF field data, ω1And ω2Are respectively as
Figure BDA0002047619230000074
And
Figure BDA0002047619230000075
noise components at the field. If the windowing position is within the optimal synchronization position range of FIG. 3, then ω is1And ω2Are all of average power
Figure BDA0002047619230000076
The noise component of (2). If the timing synchronization position is shifted left into the time domain extension region of the STF, then the portion ω must be made1So that the power component of (b) is increased, thereby causing
Figure BDA0002047619230000077
Becomes larger. If the timing synchronization position is shifted to the right, so that the range of LTF2 comes within the SIG CP, this also results in
Figure BDA0002047619230000078
Becomes larger. If the synchronization position is correct, no additional noise component is introduced
Figure BDA0002047619230000079
Is smaller. Therefore, after the coarse symbol timing synchronization position is obtained, the minimum value is obtained within a certain range
Figure BDA00020476192300000710
The position n is the precise symbol timing synchronous position.
Figure BDA00020476192300000711
Figure BDA0002047619230000081
Of course, the noise power determined here
Figure BDA0002047619230000082
Or by the ratio to the received signal power, i.e. by the signal-to-noise ratio
Figure BDA0002047619230000083
Is expressed in the form of (P)LTF1And PLTF2Signal power corresponding to both LTF1 and LTF2 for the received signal, respectively), but by looking for
Figure BDA0002047619230000084
Is the same as when the timing synchronization position is determined to be essential by finding the maximum value of snr (n).
Three frame formats are defined in 802.11n, namely Legacy, HT-Mixed, and HT-greenfield modes, all of which have common features as shown in fig. 3, fig. 3 being a schematic diagram of an 802.11n frame format according to an embodiment of the present invention. The frame header part contains an STF field and an LTF field. Wherein the STF field is composed of 10 identical time domain subfields, each subfield STF i (1 ≦ i ≦ 10) contains 16 baseband data points in the 20MHz bandwidth mode and 32 baseband data points in the 40MHz bandwidth mode. The LTF field contains two identical fields LTF1 and LTF2, with an LTF CP portion in front of the LTF, which is a copy of either the LTF1 or the second half of LTF 2. LTF1 and LTF2 each contain 64 time domain data points in the 20MHz bandwidth mode, with the LTF CP portion containing 32 data points and the SIG CP containing 16 baseband data points. In the 40MHz bandwidth mode, LTF1 and LTF2 each contain 128 time-domain data points, the LTF CP portion contains 64 baseband data points, and the SIG CP contains 32 baseband data points.
In the following implementation types, the 20MHz bandwidth mode is taken as an example, and meanwhile, the transmitting end of the 802.11n signal is assumed to use 4 antennas for transmission. Among the 3 frame formats specified in 802.11n, STF and LTF in the frame headers of Legacy and HT-Mixed formats are Non-HT mode, and STF and LTF in the frame headers of HT-Greenfield format are HT mode. The time domain cyclic shifts for Non-HT mode and HT mode OFDM symbols are defined in the standard as table 1 and table 2.
Figure BDA0002047619230000091
TABLE 1 Cyclic Shift as defined for Non-HT part 802.11n
Figure BDA0002047619230000092
Figure BDA0002047619230000101
TABLE 2 Cyclic Shift as defined for HT portion 802.11n
First mode (corresponding to mode 1 above)
Fig. 4 is a schematic diagram of LTFs of a header portion of a Greenfield format frame transmitted by 4 transmit antennas according to an embodiment of the present invention, as shown in fig. 4, and a delay spread portion of an STF10 in a multipath channel environment is shown as a shaded triangle. If the OFDM symbol length is N, the LTF CP has N/2 data points and the other SIG CP portions are N/4 data points. If the multipath delay spread of the channel does not exceed the SIG CP length, then the symbol timing synchronization position of LTF1 must be chosen within the interval L of the second half of the LTF CP.
Assuming that the signal has no carrier frequency offset at this time, after obtaining the coarse symbol timing synchronization position, the receiver obtains an interval for searching the precise symbol timing synchronization position. If the symbol timing synchronization position of LTF1 is taken at position n in fig. 4, the following sequence is followed:
first, using N/4 data points before the synchronization position
Figure BDA0002047619230000102
Figure BDA0002047619230000103
(N/4 Point data Block 1 in FIG. 4) replace the received data Point
Figure BDA0002047619230000104
(N/4 dot data block 2 in FIG. 4);
next, according to the aforementioned formula (8), there are
Figure BDA0002047619230000105
Figure BDA0002047619230000111
Partial time domain data within the window of LTF1 and LTF2 may also be used,
Figure BDA0002047619230000112
wherein M is more than or equal to 0 and less than or equal to N-G, G is the SIG CP length, and N is the OFDM symbol length. For the 20MHz bandwidth mode, N-64 and G-16. For the 40MHz bandwidth mode, N-128 and G-32.
Finally, by calculating the range of a certain symbol timing synchronization position
Figure BDA0002047619230000113
Fig. 5 is a diagram illustrating a noise power curve within a symbol timing synchronization range according to an embodiment of the present invention, such as the curve shown in fig. 5, where a position where a minimum value is located is selected as an optimal symbol timing synchronization position.
Second mode (corresponding to mode 2 above)
Fig. 6 is a schematic diagram of a partial frame header structure in Greenfield frame format according to an embodiment of the present invention, as shown in fig. 6, having STF8, STF9, STF10, LTF CP and LTF1 parts. Where L represents the interval of the correct symbol timing synchronization position of LTF 1. After obtaining the coarse symbol timing synchronization position, the receiver obtains an interval for searching for the fine symbol timing synchronization position. If the received signal has no carrier frequency offset at this time, assuming that the currently searched synchronous position is n, the received data is utilized
Figure BDA0002047619230000114
Instead of in equation (8)
Figure BDA0002047619230000115
By using
Figure BDA0002047619230000116
Instead of in equation (8)
Figure BDA0002047619230000117
To obtain
Figure BDA0002047619230000118
Wherein, N is the OFDM symbol length, and G is the length of other CPs except the frame header LTF CP. For the 20MHz bandwidth mode, N-64 and G-16. For the 20MHz bandwidth mode, N-128 and G-32.
When symbol timing is synchronizedWhen the position is searched from left to right, the left data of LTF CP contains the multipath spread energy of STF10, so that the left data is obtained
Figure BDA0002047619230000119
Larger, and obtained on the right
Figure BDA0002047619230000121
It is in the bottom state.
Reconsidering the feature of using the STF field, using
Figure BDA0002047619230000122
Figure BDA0002047619230000123
Instead of rLTF1k in equation (8), use is made of
Figure BDA0002047619230000124
As in equation (8)
Figure BDA0002047619230000125
To obtain
Figure BDA0002047619230000126
When the symbol timing synchronization position is searched from left to right, the selected STF10 field may enter the LTF CP interval, so that the result on the right side is
Figure BDA0002047619230000127
Larger, and obtained on the left
Figure BDA0002047619230000128
It is in the bottom state.
Combining the two obtained noise powers to obtain
Figure BDA0002047619230000129
Typically, take α to 1 and,
Figure BDA00020476192300001210
still with the feature of fig. 5, the position where the minimum value is found is the best position for symbol timing synchronization.
Third mode (corresponding to mode 3 above)
In the case of the 802.11n system having a plurality of transmitting antennas, time domain cyclic shifts as shown in tables 1 and 2 are required between signals transmitted from the respective antennas. A "pseudo multipath" phenomenon may occur when cross-correlation calculations are performed using locally generated LTF symbols and the LTF symbols of the received signal to find the multipath spread of the signal. FIG. 7 is a diagram illustrating the LTF cross-correlation results obtained for Non-HT mode, in accordance with an embodiment of the present invention; fig. 8 is a diagram illustrating LTF cross-correlation results obtained in HT mode with two transmit antennas at the transmit end and four transmit antennas at the transmit end, both in 20MHz bandwidth mode, according to an embodiment of the present invention. In fig. 7, the pseudo-multipath location is shifted by 4 baseband data points forward relative to the true channel path location in the 20MHz bandwidth mode due to a-200 ns cyclic shift. In the 20MHz bandwidth mode, the positions of the three pseudo-multipaths in fig. 8 are shifted forward by 12, 8, and 4 baseband data points, respectively, with respect to the true channel path position. When timing synchronization of OFDM symbols is performed, timing synchronization errors often occur because it is not possible to distinguish whether or not pseudo multipath exists or which paths are pseudo multipath.
After the coarse timing synchronization position is obtained, the local LTF symbol is used
Figure BDA0002047619230000131
And receiving the signal
Figure BDA0002047619230000132
Performing sliding cross correlation in a certain range to obtain
Figure BDA0002047619230000133
Where x represents the conjugate and N is the length of the current OFDM symbol. When z (n) sliding ranges are located at the rear of LTF1 and the front of LTF2, multi-path spreading and energy information of each channel path can be obtained as shown in fig. 7 or fig. 8.
After the energy of multipath spreading and the delay information thereof are available, a sliding window method may be used to find the optimal synchronization position reference by finding the position with the maximum multipath energy in the window, fig. 9 is a schematic diagram of finding the synchronization position reference by using the sliding window according to the embodiment of the present invention, as shown in fig. 9, when the 802.11n system has only one transmitting antenna, an energy Ω (n) in the current window is calculated by using a sliding window with a length of G +1 (G is the length of SIG CP), and the optimal symbol timing synchronization position reference may be obtained by finding the position with the maximum energy.
Figure BDA0002047619230000134
However, when the 802.11n system has multiple transmitting antennas, there is a relative time domain cyclic shift between the corresponding signals, and the receiver does not know in advance that the transmitting end of the signal has several transmitting antennas, nor does the receiver know whether the currently received signal is in Non-HT mode or HT mode. Using only the sliding window method with length G +1 at this time will also factor in the pseudo multipath energy, possibly leading to synchronization decision errors.
As can be seen from tables 1 and 2, if the multipath has a spread length of G, the sliding window having a length of G +1 is not sufficient to cover the energy of the pseudo multipath. Since the receiver does not know the number of transmitting antennas at the transmitting end, it is considered to use 4 antennas with lengths of G +1 and G + I1+1、G+I2+1 and G + I3+1 (for 20MHz bandwidth mode, I1＝4、I2＝8、I 312. For 40MHz bandwidth mode, I1＝8、I2＝16、I324) are calculated for each sliding window of equation (15), i.e.
Figure BDA0002047619230000135
Figure BDA0002047619230000136
Figure BDA0002047619230000137
Figure BDA0002047619230000141
And respectively find omega1(n)、Ω2(n)、Ω3(n) and Ω4(n) position n where the maximum value is located1，max、n2，max、n3，maxAnd n4，max(in the range of J interval in FIG. 9).
When the transmitting end has only one transmitting antenna, n obtained by equation (16)1，max+1 is the ideal timing synchronization position reference. When there are two transmit antennas, (17) an ideal synchronization position reference can be found for the Non-HT mode signal. And for HT mode signals, equation (18) can find the ideal synchronization position reference. When there are 3 transmit antennas, (17) an ideal synchronization position reference can still be found for the Non-HT mode signals. And, for the HT mode signal, the expression (18) can still be used. When there are 4 transmit antennas, the maximum cyclic shift of the signal in Non-HT mode will have an advance of-3 baseband data points over the 20MHz bandwidth, and it is still true that equation (17) is used in most cases. For the HT mode signal, the ideal synchronization position reference can be found by equation (19).
Although the above equations (16,17,18,19) can cover all cases, the result of which equation is ultimately selected as the timing synchronization position reference remains uncertain. After the received data is precisely compensated for carrier frequency offset, as shown in fig. 9, n may be used1，max、n2，max、n3，maxAnd n4，maxFor the position reference, the noise power at the corresponding synchronization position (in the range of the L interval in fig. 9) is determined using the first type of equations (9, 10) or the second type of equations (11, 12, 13), respectively
Figure BDA0002047619230000142
And
Figure BDA0002047619230000143
and selecting the synchronization position corresponding to the minimum noise power as the optimal symbol timing synchronization position.
Through the above description of the embodiments, those skilled in the art can clearly understand that the method according to the above embodiments can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware, but the former is a better implementation mode in many cases. Based on such understanding, the technical solutions of the present invention may be embodied in the form of a software product, which is stored in a storage medium (e.g., ROM/RAM, magnetic disk, optical disk) and includes instructions for enabling a terminal device (e.g., a mobile phone, a computer, a server, or a network device) to execute the method according to the embodiments of the present invention.
Example 2
In this embodiment, a device for determining a symbol timing synchronization position is further provided, where the device is used to implement the foregoing embodiments and preferred embodiments, and details are not repeated for what has been described. As used below, the term "module" may be a combination of software and/or hardware that implements a predetermined function. Although the means described in the embodiments below are preferably implemented in software, an implementation in hardware, or a combination of software and hardware is also possible and contemplated.
Fig. 10 is a schematic structural diagram of an apparatus for determining a symbol timing synchronization position according to an embodiment of the present invention, as shown in fig. 10, the apparatus includes: a first obtaining module 1002, configured to obtain a field length of a first long code part LTF in a digital signal in an orthogonal frequency division multiplexing OFDM digital information system; wherein the first LTF comprises a second LTF and a third LTF; a second obtaining module 1004, coupled to the first obtaining module 1002, configured to obtain a first noise component of the second LTF field and a second noise component of the third LTF field, respectively; a determining module 1006, coupled to the second obtaining module 1004, is configured to determine a symbol timing synchronization position according to the field length, the first noise component, and the second noise component.
Optionally, the determining module 1006 in this embodiment is configured to determine the symbol timing synchronization position by:
Figure BDA0002047619230000151
wherein the content of the first and second substances,
Figure BDA0002047619230000152
is the noise power at symbol timing synchronization position N, N is the field length of the first LTF,
Figure BDA0002047619230000153
and
Figure BDA0002047619230000154
for the received field data, ω, of the second LTF and the third LTF1And ω2A first noise component and a second noise component; n and N are positive integers;
then, a plurality of first noise components and second noise components are obtained based on different values of n, and then a plurality of noise powers are obtained
Figure BDA0002047619230000161
The value of (1) is obtained; from multiple noise powers
Figure BDA0002047619230000162
Is determined from the value-taking result
Figure BDA0002047619230000163
The value of n at the minimum is the symbol timing synchronization position.
Alternatively, in the case where the multipath delay spread of the channel does not exceed the length of the signal cycle SIG CP in the digital signal, the determining module 1006 involved in this embodiment is configured to determine the symbol timing synchronization position by:
with N/4 data points before the synchronization position N
Figure BDA0002047619230000164
Replacing received data points in a digital signal
Figure BDA0002047619230000165
Based on the above substitution of data points, equation 1 transforms to equation 2 as follows:
Figure BDA0002047619230000166
wherein M is more than or equal to 0 and less than or equal to N-G, and G is the length of SIG CP;
and then a plurality of first noise components and second noise components are obtained based on different values of n, and then a plurality of noise powers are obtained
Figure BDA0002047619230000167
The value of (1) is obtained; from multiple noise powers
Figure BDA0002047619230000168
Is determined from the value-taking result
Figure BDA0002047619230000169
The value of n at the minimum is the symbol timing synchronization position.
Alternatively, the determining module 1004 involved in the present embodiment determines the symbol timing synchronization position by:
in the data to be received
Figure BDA00020476192300001610
Instead of in equation (1)
Figure BDA00020476192300001611
By using
Figure BDA00020476192300001612
Instead of in equation (1)
Figure BDA00020476192300001613
Equation 3 is obtained:
Figure BDA00020476192300001614
g is the length of other CPs except the frame header LTF CP in the digital signal;
further, use
Figure BDA00020476192300001615
Instead of in equation (1)
Figure BDA00020476192300001616
Use of
Figure BDA00020476192300001617
As in formula (1)
Figure BDA00020476192300001618
Equation 4 is obtained:
Figure BDA00020476192300001619
equation 5 is derived from equation 3 and equation 4:
Figure BDA0002047619230000171
wherein α is 1;
finally, a plurality of first noise components and second noise components are obtained based on different values of n, and then a plurality of noise powers are obtained
Figure BDA0002047619230000172
The value of (1) is obtained; from multiple noise powers
Figure BDA0002047619230000173
Is determined from the value-taking result
Figure BDA0002047619230000174
The value of n at the minimum is the symbol timing synchronization position.
Optionally, in case of multiple transmit antennas, the determining module is configured to determine the symbol timing synchronization position by:
local LTF symbols
Figure BDA0002047619230000175
And receiving the signal
Figure BDA0002047619230000176
Sliding cross-correlation is performed within a certain range to obtain formula 6:
Figure BDA0002047619230000177
wherein represents conjugation;
the energy in the current window Ω (n) is calculated by equation 7:
Figure BDA0002047619230000178
further, obtaining a plurality of first noise components and second noise components based on different values of n, and further obtaining value results of energy omega (n) in a plurality of current windows; and determining the value of n as the symbol timing synchronization position when the energy omega (n) is maximum from the value taking results of the energy omega (n) in the current windows.
It should be noted that, the above modules may be implemented by software or hardware, and for the latter, the following may be implemented, but not limited to: the modules are all positioned in the same processor; alternatively, the modules are respectively located in different processors in any combination.
Example 3
Embodiments of the present invention also provide a storage medium having a computer program stored therein, wherein the computer program is arranged to perform the steps of any of the above method embodiments when executed.
Alternatively, in the present embodiment, the storage medium may be configured to store a computer program for executing the steps of:
s1, acquiring the field length of the first long code part LTF in the digital signal in the OFDM digital information system; wherein the first LTF comprises a second LTF and a third LTF;
s2, respectively obtaining a first noise component of the second LTF field and a second noise component of the third LTF field;
and S3, determining the symbol timing synchronization position according to the field length, the first noise component and the second noise component.
Optionally, in this embodiment, the storage medium may include, but is not limited to: various media capable of storing computer programs, such as a usb disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic disk, or an optical disk.
It will be apparent to those skilled in the art that the modules or steps of the present invention described above may be implemented by a general purpose computing device, they may be centralized on a single computing device or distributed across a network of multiple computing devices, and alternatively, they may be implemented by program code executable by a computing device, such that they may be stored in a storage device and executed by a computing device, and in some cases, the steps shown or described may be performed in an order different than that described herein, or they may be separately fabricated into individual integrated circuit modules, or multiple ones of them may be fabricated into a single integrated circuit module. Thus, the present invention is not limited to any specific combination of hardware and software.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. A method for determining a symbol timing synchronization position, comprising:
acquiring the length of a field of a first long code part LTF in a digital signal in an Orthogonal Frequency Division Multiplexing (OFDM) digital information system; wherein the first LTF comprises a second LTF and a third LTF;
respectively acquiring a first noise component of a field of the second LTF and a second noise component of a field of the third LTF;
determining a symbol timing synchronization position according to the field length, the first noise component and the second noise component;
wherein the symbol timing synchronization position is determined by:
Figure FDA0002340364580000011
wherein the content of the first and second substances,
Figure FDA0002340364580000012
is the noise power at symbol timing synchronization position N, N is the field length of the first LTF,
Figure FDA0002340364580000013
and
Figure FDA0002340364580000014
for the received field data, ω, of the second LTF and the third LTF1And ω2The first noise component and the second noise component; n and N are positive integers;
obtaining a plurality of first noise components and the second noise components based on different values of n, and further obtaining a plurality of noise powers
Figure FDA0002340364580000015
The value of (1) is obtained;
from multiple noise powers
Figure FDA0002340364580000016
Is determined from the value-taking result
Figure FDA0002340364580000017
The value of n at the minimum is the symbol timing synchronization position.
2. The method of claim 1, wherein the symbol timing synchronization position is determined by, in the event that multipath delay spread of a channel does not exceed a length of a signal cycle SIG CP in the digital signal:
with N/4 data points before the synchronization position N
Figure FDA0002340364580000021
Figure FDA0002340364580000022
Replacing received data points rn + N-1, rn + N-2, …, rn + 3. N/4 in the digital signal;
based on the above substitution of data points, the equation 1 transforms to the following equation 2:
Figure FDA0002340364580000023
wherein M is more than or equal to 0 and less than or equal to N-G, and G is the length of SIG CP;
obtaining a plurality of first noise components and the second noise components based on different values of n, and further obtaining a plurality of noise powers
Figure FDA0002340364580000024
The value of (1) is obtained;
from multiple noise powers
Figure FDA0002340364580000025
Is determined from the value-taking result
Figure FDA0002340364580000026
The value of n at the minimum is the symbol timing synchronization position.
3. The method of claim 1, wherein the symbol timing synchronization position is determined by:
in the data to be received
Figure FDA0002340364580000027
Instead of in equation (1)
Figure FDA0002340364580000028
By using
Figure FDA0002340364580000029
Figure FDA00023403645800000210
Instead of rLTF2k in equation (1), equation 3 is obtained:
Figure FDA00023403645800000211
g is the length of other CPs except the frame header LTF CP in the digital signal;
use of
Figure FDA00023403645800000212
Instead of in said formula (1)
Figure FDA00023403645800000213
Use of
Figure FDA00023403645800000214
Figure FDA00023403645800000215
Replacing rLTF2k in equation (1) yields equation 4:
Figure FDA00023403645800000216
obtaining a formula 5 according to the formula 3 and the formula 4:
Figure FDA00023403645800000217
wherein α is 1;
obtaining a plurality of first noise components and the second noise components based on different values of n, and further obtaining a plurality of noise powers
Figure FDA0002340364580000031
The value of (1) is obtained;
from multiple noise powers
Figure FDA0002340364580000032
Is determined from the value-taking result
Figure FDA0002340364580000033
The value of n at the minimum is the symbol timing synchronization position.
4. The method of claim 1, wherein the symbol timing synchronization position is determined in the presence of multiple transmit antennas by:
local LTF symbols
Figure FDA0002340364580000034
And receiving the signal
Figure FDA0002340364580000035
Sliding cross-correlation is performed within a certain range to obtain formula 6:
Figure FDA0002340364580000036
wherein represents conjugation;
the energy in the current window Ω (n) is calculated by equation 7:
Figure FDA0002340364580000037
obtaining a plurality of first noise components and the second noise components based on different values of n, and further obtaining value results of energy omega (n) in a plurality of current windows;
and determining the value of n when the energy omega (n) is maximum as the symbol timing synchronization position from the value taking results of the energy omega (n) in the current windows.
5. An apparatus for determining a symbol timing synchronization position, comprising:
the first acquisition module is used for acquiring the field length of a first long code part LTF in a digital signal in an Orthogonal Frequency Division Multiplexing (OFDM) digital information system; wherein the first LTF comprises a second LTF and a third LTF;
a second obtaining module, configured to obtain a first noise component of a field of the second LTF and a second noise component of a field of the third LTF, respectively;
a determining module, configured to determine a symbol timing synchronization position according to the field length, the first noise component, and the second noise component;
wherein the determining module is configured to determine the symbol timing synchronization position by:
Figure FDA0002340364580000041
wherein the content of the first and second substances,
Figure FDA0002340364580000042
is the noise power at symbol timing synchronization position N, N is the field length of the first LTF,
Figure FDA0002340364580000043
and
Figure FDA0002340364580000044
for the received field data, ω, of the second LTF and the third LTF1And ω2The first noise component and the second noise component; n and N are positive integers;
obtaining a plurality of first noise components and the second noise components based on different values of n, and further obtaining a plurality of noise powers
Figure FDA0002340364580000045
The value of (1) is obtained;
from multiple noise powers
Figure FDA0002340364580000046
Is determined from the value-taking result
Figure FDA0002340364580000047
The value of n at the minimum is the symbol timing synchronization position.
6. The apparatus of claim 5, wherein the determining module is configured to determine the symbol timing synchronization position in the case that a multipath delay spread of a channel does not exceed a length of a signal cycle SIG CP in the digital signal by:
with N/4 data points before the synchronization position N
Figure FDA0002340364580000048
Figure FDA0002340364580000049
Replacing received data points rn + N-1, rn + N-2, …, rn + 3. N/4 in the digital signal;
based on the above substitution of data points, the equation 1 transforms to the following equation 2:
Figure FDA0002340364580000051
wherein M is more than or equal to 0 and less than or equal to N-G, and G is the length of SIG CP;
obtaining a plurality of first noise components based on different values of nAnd the second noise component, thereby obtaining a plurality of noise powers
Figure FDA0002340364580000052
The value of (1) is obtained;
from multiple noise powers
Figure FDA0002340364580000053
Is determined from the value-taking result
Figure FDA0002340364580000054
The value of n at the minimum is the symbol timing synchronization position.
7. The apparatus of claim 5, wherein the means for determining determines the symbol timing synchronization position by:
in the data to be received
Figure FDA0002340364580000055
Instead of in equation (1)
Figure FDA0002340364580000056
By using
Figure FDA0002340364580000057
Figure FDA0002340364580000058
Instead of rLTF2k in equation (1), equation 3 is obtained:
Figure FDA0002340364580000059
g is the length of other CPs except the frame header LTF CP in the digital signal;
use of
Figure FDA00023403645800000510
Instead of said formula(1) In (1)
Figure FDA00023403645800000511
Use of
Figure FDA00023403645800000512
Figure FDA00023403645800000513
Replacing rLTF2k in equation (1) yields equation 4:
Figure FDA00023403645800000514
obtaining a formula 5 according to the formula 3 and the formula 4:
Figure FDA00023403645800000515
wherein α is 1;
obtaining a plurality of first noise components and the second noise components based on different values of n, and further obtaining a plurality of noise powers
Figure FDA00023403645800000516
The value of (1) is obtained;
from multiple noise powers
Figure FDA00023403645800000517
Is determined from the value-taking result
Figure FDA00023403645800000518
The value of n at the minimum is the symbol timing synchronization position.
8. The apparatus of claim 5, wherein the means for determining is configured to determine the symbol timing synchronization position in the presence of multiple transmit antennas by:
local LTF symbols
Figure FDA0002340364580000061
And receiving the signal
Figure FDA0002340364580000062
Sliding cross-correlation is performed within a certain range to obtain formula 6:
Figure FDA0002340364580000063
wherein represents conjugation;
the energy in the current window Ω (n) is calculated by equation 7:
Figure FDA0002340364580000064
obtaining a plurality of first noise components and the second noise components based on different values of n, and further obtaining value results of energy omega (n) in a plurality of current windows;
and determining the value of n when the energy omega (n) is maximum as the symbol timing synchronization position from the value taking results of the energy omega (n) in the current windows.
9. A storage medium, in which a computer program is stored, wherein the computer program is arranged to perform the method of any of claims 1 to 4 when executed.
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